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United States Patent |
6,232,513
|
Hub
,   et al.
|
May 15, 2001
|
Isomerization of hydrofluorocarbon
Abstract
In order to isomerize a hydrofluorocarbon having a certain thermodynamic
stability (HFC 1) into a hydrofluorocarbon of greater thermodynamic
stability (HFC 2), the hydrofluorocarbon HFC 1 is subjected to a heat
treatment in the presence of hydrogen at a temperature above 500.degree.
C.
This process, which does not require the use of a catalyst, applies
especially to the isomerization of 1,1,2,2-tetrafluoroethane into
1,1,1,2-tetrafluoroethane.
Inventors:
|
Hub; Serge (Villeurbanne, FR);
Guillet; Dominique (Vernaison, FR)
|
Assignee:
|
Elf Atochem S.A. (Paris, FR)
|
Appl. No.:
|
341760 |
Filed:
|
December 22, 1999 |
PCT Filed:
|
January 9, 1998
|
PCT NO:
|
PCT/FR98/00035
|
371 Date:
|
December 22, 1999
|
102(e) Date:
|
December 22, 1999
|
PCT PUB.NO.:
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WO98/31650 |
PCT PUB. Date:
|
July 23, 1998 |
Foreign Application Priority Data
Current U.S. Class: |
570/151 |
Intern'l Class: |
C07C 019/08 |
Field of Search: |
570/151
|
References Cited
U.S. Patent Documents
2315871 | Apr., 1943 | Oberfell et al.
| |
4902838 | Feb., 1990 | Manzer et al.
| |
4950815 | Aug., 1990 | Moore et al.
| |
5030372 | Jul., 1991 | Manogue et al. | 570/151.
|
5091600 | Feb., 1992 | Moore et al.
| |
Foreign Patent Documents |
365296 | Apr., 1990 | EP.
| |
2-115135 | Apr., 1990 | JP.
| |
3-261731 | Nov., 1991 | JP.
| |
WO 95/15300 | Jun., 1995 | WO.
| |
Primary Examiner: Siegel; Alan
Attorney, Agent or Firm: Smith, Gambrell & Russell
Parent Case Text
This application is a 371 of PCT/FR98/00035 filed Jan. 9, 1998.
Claims
What is claimed is:
1. Process comprising isomerization of a hydrofluorocarbon having a certain
thermodynamic stability (HFC 1) into a hydrofluorocarbon of greater
thermodynamic stability (HFC 2), the hydrofluorocabon (HFC 1) is heat
treated in the presence of hydrogen at a temperature above 500.degree. C.
2. Process according to claim 1, in which the reaction is carried out at a
temperature of between 500 and 1000.degree. C.
3. Process according to claim 1, wherein the reaction is carried out at a
pressure of between 0.1 and 50 bar.
4. Process according to claim 1, wherein the hydrogen/hydrofluorocarbon
(HFC 1) molar ratio is between 1 and 100.
5. Process according to claim 1, wherein the reaction is carried out in an
empty reactor made of metal or quartz.
6. Process according to claim 1, wherein the hydrofluorocarbon to be
isomerized (HFC 1) is 1,1,2,2-tetrafluoroethane.
7. Process according to claim 2, wherein the temperature is between 600 and
750.degree. C.
8. Process according to claim 3, wherein the pressure is from atmospheric
up to 20 bar.
9. Process according to claim 4, wherein the molar ratio is between 2 and
20.
Description
FIELD OF THE INVENTION
The subject of the present invention, which relates to the field of
fluorinated hydrocarbons, is the isomerization of hydrofluorocarbons (HFC)
and, more particularly, that of 1,1,2,2-tetrafluoroethane (F134) into
1,1,1,2-tetrafluoroethane (F134a).
BACKGROUND OF THE INVENTION
F134a is one of the hydrofluorocarbons (HFC) falling within the context of
the replacement of the chlorofluorocarbons (CFC) and
hydrochlorofluorocarbons (HCFC) which have already been banned or are in
the process of being banned because of their harmful effect on the
stratospheric ozone layer.
Several ways of obtaining F134a are known, namely:
the fluorination of 1-chloro-2,2,2-tri-fluoroethane (F133a) in gas or
liquid phase;
the fluorination of trichloroethylene in liquid phase;
the hydrogenolysis of 1,1-dichloro-1,2,2,2-tetrafluoroethane (F114a) or of
1-chloro-1,2,2,2-tetrafluoroethane (F124);
the isomerization of 1,1,2,2-tetrafluoroethane (F134).
According to the literature, the latter process is carried out using
catalysts. Thus, Patents EP 365,296 and JP 03 261731 describe the use of
chromium-based catalysts and U.S. Pat. No. 4,902,838 claims a catalyst of
the fluorinated alumina type; Patent JP 02 115135 prefers to use a
catalyst of the aluminium chlorofluoride type. The use of a catalyst is
not always sufficient; thus, U.S. Pat. No. 4,902,838 recommends
introducing oxygen into the medium so as to maintain the catalytic
activity over time and Patent Application WO 95/15300 recommends
introducing a source of chloride ions.
DESCRIPTION OF THE INVENTION
It has now been found that it is possible to isomerize F134 into F134a
without the aid of a catalyst, by a simple heat treatment in the presence
of hydrogen. This method may also apply to the isomerization of other
HFCs, for example to that of 1,1,2-trifluoroethane (F143) into
1,1,1-trifluoroethane (F143a) or to that of 1,2-difluoroethane (F152) into
1,1-difluoroethane (F152a).
The subject of the present invention is therefore a process for the
isomerization of a hydrofluorocarbon having a certain thermodynamic
stability (HFC 1) into a hydrofluorocarbon of greater thermodynamic
stability (HFC 2), characterized in that the hydrofluorocarbon HFC 1 is
subjected to a heat treatment in the presence of hydrogen at a temperature
above 500.degree. C.
The process according to the invention is advantageously carried out at a
temperature of between 500 and 1000.degree. C., preferably between 600 and
750.degree. C.
The pressure of the reaction may be between 0.1 and 50 bar, but it is
preferred to work between atmospheric pressure and 20 bar.
The H.sub.2 /HFC 1 molar ratio may range from 1 to 100, but it is generally
preferred to work with a molar ratio of between 2 and 20. The flux of
reactants (HFC 1 and H.sub.2) entering the reactor may be diluted with an
inert gas, such as helium or nitrogen.
The residence time of the reactants in the hot part of the reactor may vary
over wide ranges. It varies inversely with the temperature and is
generally between 0.1 and 1000 seconds, preferably between 1 and 300
seconds.
The isomerization may be carried out in an empty reactor, i.e. a reactor
which contains no packing but which may, however, be equipped with
thermocouples and baffles. The reactor may be made of quartz or metal. In
this case, the metal of the material forming the reactor may be chosen
from metals such as nickel, iron, titanium, chromium, molybdenum, cobalt
and gold, or their alloys. The metal, chosen more particularly for
limiting the corrosion or the catalytic phenomena, may form a solid wall
or it may be plated onto another metal, as in the case of a reactor
gold-plated on its internal surface.
EXAMPLES
The following examples illustrate the invention without limiting it.
Examples 1 to 3
Trials were carried out at atmospheric pressure in a quartz tube reactor,
having a length of 47 cm and an internal diameter of 2.1 cm, placed in an
electric furnace having a power of 1.5 kW; the temperature of the furnace
was measured using a thermocouple.
The reactants (F134 and H.sub.2) were introduced simultaneously via mass
flow meters allowing the flow rates, and therefore the molar ratios, to be
controlled.
The gaseous products were analysed by in-line chromatography (GC) at the
outlet of the reactor.
The following table summarizes the operating conditions and the results
obtained.
EXAMPLE 1 2 3
Operating conditions:
temperature (.degree. C.) 700 700 700
H.sub.2 flow rate (mmol/h) 509 187.1 29.9
F134 flow rate (mmol/h) 50.4 96 31.7
residence time (s) 10 21 95
Results:
conversion of F134 23% 27% 47%
F134a selectivity 81% 82% 81%
Examples 4 to 6
Trials were carried out at atmospheric pressure in a quartz tube reactor,
having a length of 47 cm and an internal diameter of 1.5 cm, placed in an
electric furnace having a power of 1.5 kW; the temperature of the furnace
was measured using a thermocouple.
The following table summarizes the operating conditions and the results
obtained:
EXAMPLE 4 5 6
Operating conditions:
temperature (.degree. C.) 700 700 700
H.sub.2 flow rate (mmol/h) 301.3 141.5 59.8
F134 flow rate (mmol/h) 15.2 15.2 15.2
residence time (s) 4.9 9.9 20.6
Results:
conversion of F134 13% 24% 38%
F134a selectivity 84% 78% 79%
Example 7
The operation was carried out as in Examples 1 to 3, but by replacing the
quartz reactor with a reactor made of Inconel 600 of the same size. By
working under the following operating conditions:
temperature 700.degree. C.
H.sub.2 flow rate 29.9 mmol/h
F134 flow rate 31.7 mmol/h
residence time 95 seconds
a conversion of F134 of 44% and an F134a selectivity of 74% were obtained.
Comparative Examples 8 and 9
The operation was carried out in the same way as in Examples 1 to 3, but by
replacing the hydrogen with helium. The following table summarizes the
operating conditions and the results obtained:
EXAMPLE 8 9
Operating conditions:
temperature (.degree. C.) 700 700
He flow rate (mmol/h) 312.1 35.3
F134 flow rate (mmol/h) 22.3 31.7
residence time (s) 18 95
Results:
conversion of F134 3% 15%
F134a selectivity 33% 60%
Although the invention has been described in conjunction with specific
embodiments, it is evident that many alternatives and variations will be
apparent to those skilled in the art in light of the foregoing
description. Accordingly, the invention is intended to embrace all of the
alternatives and variations that fall within the spirit and scope of the
appended claims. The above references are hereby incorporated by
reference.
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